4.4.2. Lactobacillus characteristics
Cells of the Lactobacillus genus can vary from long and slender rods to short coccobacilli rods (Hammes and Hertel, 2009). Colony morphologies also vary, but are typically convex, smooth, and opaque without pigment (Hammes and Hertel, 2009). The bee-associated Lactobacillus are negative for catalase and sporulation, positively Gram-staining, and produce lactic acid by homofermentation (Olofsson and Vásquez, 2008). The Lactobacillus kunkeei clade is fructophilic, preferentially utilizing fructose over glucose as the carbon source (Neveling et al., 2012).
Lactobacillus species are ubiquitous in nature and are commonly found in association with many animals, plants, and foodstuffs. Lactobacilli are widely considered probiotic, meaning their presence is beneficial to the health of the host organism (Kleerebezem and Vaughan, 2009). The bee-associated Lactobacillus fall into two main clades, “Firm-4” and “Firm-5” (Babriendier et al., 2007; Martinson et al., 2011; Moran et al., 2012). These clades are only distantly related to other Lactobacillus, with 16S rRNA identities ~90% (Olofsson and Vásquez, 2008; Vásquez et al., 2012), and thus may eventually be classified as novel species.
Another species, L. kunkeei, may be the most frequently recovered member of Lactobacillus in culturing experiments (Tajabadi et al., 2011; Vásquez et al., 2012; Neveling et al., 2012). However, culture-independent studies show “Firm-4” and “Firm-5” are the dominant bee gut lactobacilli, not L. kunkeei (Moran et al., 2012; Ahn et al., 2012). L. kunkeei has also been found on flowers (Neveling et al., 2012) and wine (Edwards et al., 1998), suggesting they may have other naturally occurring habitats outside the bee gut (McFrederick et al., 2012). Lactobacillus is the most abundant group in the bee gut and has been estimated to comprise 20-99% of bacteria in individual workers (Moran et al., 2012).